Bound

The creature is magically bound to an amulet. As long as the creature and its amulet are on the same plane of existence, the amulet's wearer can telepathically call the creature to travel to it, and the creature knows the distance and direction to the amulet. If the creature is within 60 feet of the amulet's wearer, half of any damage the wearer takes (rounded up) is transferred to the creature. (Shield Guardian, pp. 271, MM)